Periodic wave-generating system



Dec. 31, 1940.. c lN 2,226,706

' PERIODIC WAVE-GENERATING SYSTEM Filed Nov. 29,- 1937 2 Sheets-Sheet 1l0 ll l2 l3 $33 9 RELAXATION DIFFERENTIATIMIIG RELAXATION E E m'oOSCILLATOR v CIRCUIT OSCILLATOR mrwumuw INVENTOR ATTORNEY.

" M msou CAWE I Dec. 31, 1940.

M. CAWEIN PERIODIC WAVE-GENERATING SYSTEM 2 Sheets-Sheet 2 Filed Nv. 29;1937' zorrdxjum INVENTOR. M OISON cAwE BY A 2:4

ATTORNEY v mmiom Gui- OWO Patented Dec. 31 1540 ,zaros I 2,226,706PERIODIC WAVE-GENERATING SYSTEM Madison Cawein, liianhasset, N. E,assignor to Hazeltine (lorporation, a corporation of DelawareApplication November 29, 1931, Serial No. 176,963

20' Claims. (oi. 1784.2)

This invention relates to periodic wave-gen-v .erating'systems such asare adapted for use in television systems and, particularly, to improvedsystems for developing two periodic impulse 5 waves which are displacedin phase in a predetermined manner and to a predetermined extent.

In certain signaling systems, such as television transmitters, it isfrequently necessary to pro.- vide a periodic wave comprisingperiodicvoltage impulses and delayed'in phase with respect to anotherperiodic voltage-impulse wave. One example of such use is in certaintypes of television systems which employ so-called interlaced scan--ning; In such systems, the scanning synchronizing signal may compriselineand framefrequency impulses, the latter being of the serrated typeand of a frequency equal to a frac-' tionalmulti-ple or aliquant of theline-frequency In order to combine the irame-ireimpulses. lo quen'cyimpulses and the line-frequency impulses without disturbing theline-frequency impulses, in a double interlaced system, the latter aredoubled during a part of the retrace portion of each framescanning cycleand impulses of 25 parabolic wave form are inserted between certain of.the double line-frequency impulses,;producing,in efiect, a singleframe-frequency impulse having serrations in which double linefrequencyimpulses are inserted. In order to 30 control the line doubling and theparabolic impulse insertion, so that they occur at the-proper times inthe frame-scanning cycle, there are developed other periodicvoltage-impulse waves of the frame frequency, but delayed in phase with35 respect to the frame-scanning wave. Heretofore, phase delays ofperiodic voltage-impulse waves of the characterreferred to have beenobtained by the use of various types of filter networks. Such apparatus,however, has been found unsuit- 40 able for obtaining the preciselytimedyrelatively long, delaysrequired in television scanning systems.

It is an object of the invention, therefore, to provide improved meansfor developing from a 45 first periodic impulse wave a second periodicimpulse wave delayed in phase with respect to the first wave. 4

It is a further object of the invention to provide an improved systemfor developing a tele- 50 vision scanning synchronizing signal.

In accordance with the invention, a periodicimpulsewave-generating-system comprises means for deriving from a, firstperiodic-impulse wave ofa predetermined frequency a secondperiodicimpulse wave having impulses initiating at the occurrences ofthe impulses of said first wave and ofa predetermined durationindependent of the duration of the impulses of the first wave. Thesystem also includes means coupled to the above- -mentioned means for.synchronization by the 5 wave developed thereby for developing a thirdperiodic-impulse wave comprising impulses initiating at the terminationof the impulses of the second wave and having a duration independent ofthe.duration of any of theother of said impulses.

In accordance with one embodiment of the present invention, there isprovided a signalgenerating system including a first generating meansfor developing a periodic impulse wave of a predetermined frequency anda second generating means for developing a wave havin 13 riodic positiveimpulses of rectangular wave form and .o predetermined duration. Thesecond generating means is so controlled by the first '20 that therectangular impulses are initiated at the leading edge of the impulsesof the first wave. Differentiating means are provided for deriving fromthe rectangular impulse waves a periodic Wave of double-impulse form,the positive and negative peaks of which occur, respectively,simultaneously with the leading and trailing edges of the rectangularimpulses. A third generating means, developing a wave of periodicimpulses of a desired wave form, is so coupled to the double-impulsewave-generating means as to be synchronized by the second and negativepeaks of the double impulses, so that the 1m.- pulses of the third waveare initiated-simultaneously therewith. The third periodic-impulse waveis thus of the same frequency as that of the first periodic-impulsewave, but delayed in phase with respect thereto by an amount equal tothe. duration of a rectangular impulse of the second generated wave. p l

In one embodiment, the invention is utilized for developing asynchronizing signal of the serrated-impulse typein a televisiontransmitting system employing interlaced scanning. In such a system, thewave developed by the first gencrating means is at the frame frequencyand the delayed-impulse wave derived therefrom is uti- 'lized to controlthecombining of the alternate line-frequency'impulses and parabolicimpulses with the line-frequency synchronizing impulses in the properrelation to develop a combined synchronizing signal including bothlineand frame-frequency impulses, the latter being 561'- rated to permituninterrupted line-frequency impulses.

double frequency. For the purpose of deriving the last-mentioned wave,there is developed a periodic wave of saw-tooth wave form and of thepredetermined double frequency, for example, by integrating therectangular-impulse wave. A periodic wave of parabolic wave form isderived from the saw-tooth wave, for example, by integrating the latterand suitable means are prcvided for limiting and amplifying theparabolic wave to derive the desired periodic wave of parabolic-impulsewave form with the impulses occurring between the rectangular impulsesof the first-mentioned wave and, hence, between the line-scanning andalternate impulses.

For a better understanding of the invention, together with other andfurther objects thereof,

reference may be had to the following detailed description taken inconnectionwith the accompanying drawings, and its scope will be pointedout in the appended claims.

In the accompamving. drawings, Fig. 1' is a diagram illustratingschematically apparatus embodying the invention; Figs. 2-5, inclusive,are

curves illustrating the wave forms 'of periodic 7 Voltage wavesdeveloped at different points in the system of Fig. 1; Fig. 6 is acircuit diagram, partially schematic, of a complete televisiontransmitting system embodying the invention; and Figs. 7-16, inclusive,are curves illustrating the wave forms of waves developed at variouspoints in the system of Fig. 6, to aid in the understanding'of theinvention.

Referring more particularly to Figs. 1-5, inclusive, in accordance withthe present invention there is provided a timing-impulse generator IIIfor developing a periodic voltage-impulse wave of a desiredpredetermined frequency and which may be of a form such as isillustrated in Fig. 2. A relaxation oscillator H is provided fordeveloping a periodic impulse wave of rectangular wave form asillustrated, for example, in Fig. 3, the wave being of the samefrequency as the wave developed by the generator ill. The oscillator IIis suitably coupled to the output circuit of the generator-l0 to besynchronized thereby so that each rectangular impulse generated byoscillator II is initiated at the occurrence of an impulse of the waveof Fig. 2. Each of the rectangular impulses deve. oped by the oscillatorII is of a predetermined duration which is independent of the durationof the impulses developed by generator l0 and isthe determining factorin the delay to be obtained. A voltage-differentiating circuit I2 isprovided for difi'erentiating the rectangular-impulse wave to derivetherefrom a double-impulse wave, such as is shown in Fig.

-4, the positive and negative peaks of the wave occurring, respectively,simultaneously with the s leading and trailing edges of the rectangularimpulses of Fig. 3. A final relaxation oscillator I! is provided fordeveloping a third periodic-impulsewave which may bear any desired waveform, for example, rectangular as shown in Fig.

5, and ofthe same frequency as the first wave,

the impulses of the wave form of oscillator i3 having a durationindependent of the durations of the impulses of any of the other waveforms. The oscillator I3 is so coupled to the differentiating circuit asto be synchronized by the negative peak or second peakof each of thedouble impulses, that is, so that the impulses of the final 'wave areinitiated upon the occurrence of the second and negative peaks of thedouble'impulses which correspond to the terminations or trailing edgesof the rectangular impulses of the wave of Fig. 3. Thefinal'pericdic-impulse wave, therefore, is delayed in phase with respectto the first wave by an amount equal to the.

. Referring now more particularly to Fig. 6 of the drawings, there isillustrated a television transmitting system comprising a cathode-raysignal generator ll which may be of conventional design and includes theusual signal-generating tube, camera, and scanning elements. Fordeveloping scanning voltages or currents for the generator l4, thereare'provided a line-frequency saw-tooth wave generator I5 and afieldfrequency saw-tooth wave generator IS, the output circuits of thesegenerators being connected to the scanning elements of the signalgenerator H in the usual manner. In order to block out the cathode rayof the generator i4 during the retrace scanning periods. there isprovided a block-out wave generator I 1 having its output circuitsuitably connected 'to the signal generator II. For providing pedestalimpulses to suppress undesirable signal impulses during retrace scanningperiods and to ensure the proper form of the modulation signal to bedeveloped,

quency impulse generator 20: parabolic-impulse wave-generating apparatusincluding a sawtooth wave generator 2|, a parabolic wave generator-2la,and limiters and amplifiers MD and 2lc connected in cascade, in theorder named; and a signal-combining network indicated generally at 22.Time-delay apparatus embodying the present inventionand corresponding tothat shown in Fig. 1 is provided in connection with the combiningnetwork and includes a relaxation oscillator llc, a differentiatingcircuit l2a,'and a relaxation oscillator Ila, which operate inconnection with the generator 20, and a'relaxation oscillator llbincluding therein a differentiating circuit l2b, and a relaxationoscillator lib, which operate in connection with the generator 2| andwill be described in detail hereinafter.

' For the p of synchronizing generators i5-2l, inclusive, and theoscillators Ha and Hb, in a manner corresponding to, the synchronizationof oscillator H lay-generator III of Fig. 1, there is provided for thesystem a timing-impulse generator 24 having the input circuits of thegenerators .ll-2l, inclusive, and oscillators Ila, lib coupled thereto.Preferably, the generators ll, 20. and 2| are all connected to a singleoutput circuit of the generator '24 across which the. latter generatoris adapted to develop a periodic wave of rectangular-impulse wave formand of double the desired line-scanning frequency, for example, 26,460cycles. The genline frequencies.

erators i9 and 26 are arranged to be synchronized by successive-impulsesof'the wave, while the generator 25 develops a wave of the double linefreguency. The generator 24 is preferably stabilizedby means of aconnection 25 to a suitable source of periodic voltage, for example, tothe power supply circuit or to the synchronizing voltage source of amotion picture mechanism, where such is employed.

- Connected in cascade to the output circuit of the cathode-ray signalgenerator id, in the order named, are video-frequency amplifiers 26, 27,and 28, a modulator 29 and associated coupled oscillator 30, a poweramplifier 3i, and an antenna system 32, 33, all according toconventional practice. The output circuit of the pedestal generator i8is coupled to the video-frequency amplifier 2?, while the output circuitof the combining network 22 is coupled to the video-frequency am-ipllfier 28.

Neglecting for the moment the details of the synchronizingsignal-generating apparatus and parts of the system associated therewithin accordance with the present invention, the system just describedcomprises the elements of a televisionltransmitting system ofconventional design and, the various parts thereof illustratedschematically being of any well-known construction, a detaileddescription of the general system and its operation is unnecessary.Briefly, how-- ever, the image of a scene to be transmitted is focusedon the target of the cathode-ray tube of the signal generator it, inwhich tube a cathode ray is developed, focused, and accelerated towardthe target in the usual manner. Scanning or deflecting currents or.voltages developedby the generators i and it are applied to the scanningelements oi the generator id to provide electric fields which serve todeflect the cathode ray horizontally and vertically, thereby to scansuccessive series of parallel lines or fields upon the target. Thedeflecting currents or voltages and, hence, the scanning fields are ofwell-known sawtooth wave form, providing a relatively slow linear traceand rapid retrace. The number of lines per field are determined by therelative field and Block-out impulses developed by the generator I! areapplied to a control electrode of the cathode-ray tube to suppress orblock out the beam during retrace portions of the scanning cycles, whilepedestal impulses developed by the generator 3 are applied to theamplifier 21 to modify the shape of the resultant video-frequency wavedeveloped to aid in separation of lineand frame-frequency synchronizingimpulses at the receiver.

The synchronizing impulses developed by the generators i9, 20, and 2l2lcand the apparatus associated therewith are combined in the network 22and injected in the modulation amplifier 28, timing impulses developedby the generator 24 being. applied to the generators I5-2i, inclusive,to lock these generators in synchronism.

The photosensitive elements of the target in V the cathode-ray tube ofthe generator ll being electrically afiected to an extent depending uponthe varying values of light and shade at the corresponding incrementalareas 'of the images focused thereon, as the cathode ray scans thetarget a video-frequency voltage of correspondingly varying amplitude isdeveloped in'the output circuit of the generator H and applied to thevideo-frequency amplifier 26, wherein this voltage is'a'mplified andfrom which it is translated to the amplifier 21. Here thevideo-frequency voltages are further amplified and mixed with thepedestal impulses supplied from the generator IS. The mixed amplifiedvoltages in the output circuit or the amplifier 21 are thereupon appliedto the amplifier 28, wherein they are further 6 amplified and mixed withthe synchronizing impulses supplied from the combining network 22. Themodulation voltages are then supplied to the modulator 29,'wherein theyare impressed on the carrier wave generated by the oscillator 30 and theresultant modulated-carrier signal is delivered to the power amplifier3! for amplificationand is thereafter impressed upon the antenna system32, 33 to be broadcast.

Referring now more particularly to the apl5 paratus embodying thepresent invention and the circuits associated therewith, the relaxationoscillator chains ilai2a-i3a and ilb-l2b--i3b' may be entirely similarso that only one need be described in detail. The oscillator lib isconventional in form, but also embodies the differentiating circuit MD,in accordance with the present invention. I More particularly, thisoscillator includes a condenser 60 and an inductance M in series, thelatter having an impedance which is relatively verysmall compared tothat of the condenser at the oscillation frequency. A charging circuitis provided for the condenser QB which includes a source of directcurrent, for example, a battery 62 preferably grounded at its 3 negativeterminal, a resistor t3, and the space current path of a vacuum tube 45.A discharge circuit comprising an adjustable resistor 85 is connectedacross the condenser for discharging it at a predetermined rate. Aregenerating tube 35 as is provided in connection with the tube 46,having its cathode'grounded and its anode connected to the controlelectrode of the tube 445. The control grid of the regenerating tube 66is connected by way of a suitable coupling con-- 40 denser 41 to theanode of tube 44. Abufier amplifier tube 58 is interposed between theoscillator, per se, and the timing-impulse generator 24 to which it iscoupled by way of a suitable coupling condenser 49 to receivesynchronizing or 45 control impulses ,of frame-synchronizing irequency.Suitable grid-leak resistors'50 are connected between the controlgrids-and cathodes of the tubes 46 and 48, while operating potentialsmay be supplied to the anodes ofthesetubes 50- from the positiveterminal of a battery 5| by wayof a common load resistor 52.

The differentiating circuit is here provided by the inductance I of theoscillator lib and a secondary winding 53 coupled thereto which is, inturn, coupled by way of a suitable condenser 54 to, theinput circuit ofthe oscillator l3b for synchronizing the operation thereof.

.The relaxation oscillator I3!) is of substantially the sameconstruction and operation as the 0 oscillator llb, similar elementsbeing designated by the same reference numerals with the sufiix a.However, in generator I31) a resistor 55 is included in series with thecharging condenser 40a instead of an inductance and the output circultof the oscillator is connected across the resistor 55 and coupled, byway ot a suitable condenser 56, to the suppressor grid of the tube 36.In the operation of the generator. lib (and similarly of the oscillatorltb), the condenser 40 is rapidly charged from the source 42 by way ofthe tube 44 and is discharged at a relatively upon the application of asynchronizing'impulse rivative of the saw-tooth voltage wave.

veloped across the load resistor 52 and applied to the control grid ofthe tube 44 to accelerate the charging action. The synchronizing ortiming impulses, supplied from the generator 24 and applied to thecontrol grid of the tube 44, by way of the condenser 49 and buiferamplifier 4l, serve to synchronize the operation of the oscillator atthe frame-synchronizing frequency.

. The periodic charging an discharging of the condenser causes a volt geto be developed.

thereacross which has a saJw-tooth wave form and, hence, a current flowsthrough the condenser 40 and inductance 4| which has a periodicrectangular-impulse wave form. such as is shown in Fig. 3, that is,which is the first de- The reactance voltage drop across the inductance4| is the first derivative of the current therethrough and, hence, is ofthe double-impulse form shown in Fig. 4. This voltage is induced in thewinding 53 and is so impressed upon the input circuit of the oscillatorl3b that the second impulse of each double impulse thereof is a negativeimpulse and serves as a synchronizing impulse for this oscillator. Theoscillator lib operates in substantially the same way as the oscillatorllb, except that, since the resistor 55 is included in series with thecondenser 40a instead of an inductance, the voltage developed acrossthis resistor is of the same wave form as the current through thecondenser 44 and resistor, that is, of the periodic rectangular-impulsewave form as shown in Fig. 5. Since the periodic rectangular-impulsewaves developed, by the oscillator l3b are synchronized or initiated bythe second and negative peaks ofthe double impulses developed across theinductance 4|, it will be appreciated that the leading edges of therectangular impulses of the wave across resistor 55 are delayed in phasewith respect to the leading edges of the current impulses throughcondenser 40 by amounts equal to the duration of a current impulsethrough condenser 44.

The duration of the rectangular impulses developed by the oscillatorsllb and lib may be suitably determined by adjustment oi the circuitconstants of these oscillators. For example, the resistance of the tube44 when conductive is very low and may be arbitrarily indicated by r andthe period of the generated wave may be taken as unit time or 1, withthe trace part of the cycle indicated as a fraction, b. The duration ofthe rectangularimpulse, which is equal, in time, to the retrace part ofa cycle, therefore, is 1-b. When proper circuit adjustments exist,

' or, more conveniently, the value of R. In order to obtain relativelylarge adjustments, while still maintaining stable oscillations,.it maysometimes be necessary to adjust the capacitance of the impulse may beessay/0c wave being of double the desired line-scanning frequency, forexample, 26,460 cycles. The sawtooth wave generator may comprise asuitable circuit for deriving from the rectangular impulse wave asaw-tooth wave, such as is illus- ..trated in Fig, 13, of the samefrequency as the rectangular-impulse wave and with its retrace portionsoccurring during the rectangular impulses.- The parabolic wave generator2m comprises suitable circuits for deriving, from the saw-tooth wave, awave of the same frequency and of parabolic wave form, such as isillustrated in Fig. 14, with the positive portions thereof occurringduring the trace periods of the saw-tooth wave. The circuits of thegenerators II and Ila preferably comprise integration circuits, as, forexample, high impedance pentode tubes having capacitance elementsincluded in their anode circuits whereby the voltages impressed upontheir input circuits cause currents of similar wave form to flow intheir anode circuits and voltages to be developed across the capacitanceelements having wave forms which are infinitesimal cal- The limiter andamplifier Zlb may comprise a conventional vacuum tube having its gridcircuit 'so biased as to cut 01! a portion oi the parabolic waveimpressed on its input circuit, for example, the portion indicated belowthe brokenline in Fig. 14, thereby to develop a wave of parabolicimpulsewave form, such as illustrated by the curve of Fig. 15. The limiter andamplifier He may comprise apparatus similar to that 01. the limiter andamplifier 2lb and be similarly arranged to cut off a portion of the waveimpressed upon its input circuit, as, for example, the portion indicatedbelow the broken line in Fig. 15, and to amplify this wave, thereby todevelop a wave of the double line frequency and of truncatedparabolic-impulse wave form such as is illustrated by the curve of Fig.15. It will be noted that the impulses oi the last-mentioned wave occurbetween the rectangular impulses of the first wave from thetiming-impulse generator. The line-synchronizing impulses and alternateline impulses which are developed by the generators I! and 24,- on theother hand, as stated above, occur at the same time as. or in phasewith. corresponding impulses of the double-impulse wave. These relationsare correct for the purpose of developing the final composite serratedsynchronizing wave, as will be apparent from the description of thegeneral operation of the system hereinafter set forth.

The combining network 22 includes three pentode amplifier tubes 34, II,and II. The output circuits of the generators II and II and the limiterand amplifier Ilc are coupled, respectively, to the control'grid's oftubes I4, II, and 84. while the anode circuits of these tubes areconnccted in parallel and coupled to the amplifier 24 by way of asuitable coupling condenser 31. Operating potentials are supplied to theanodes of the tubes, by way of a load resistor II and choke 3!, and

aaaenoc to their screens from suitable sources indicated, respectively,at +B and +80. The'suppressor grid of the tube 34 is connected inconventional manner to its cathode, while the suppressor grids of thetubes 35 and 36 are normally biased sufficiently negative to renderthese tubes nonconductive, as by means of suitable batteries 23 and leakresistors 23a. The suppressor grids of the tubes 35 and 36 are alsocoupled to the output circuits of the oscillators I30. and I3b,respectively.

,In considering the general operation of the scanning synchronizingsystem, reference will be had to the curves of Figs. 7-11, inclusive,which show the wave forms of the currents or voltages developed atdifferent points in the system. The curve of Fig. '7 represents thesignal appearing at the output of the video-frequency amplifier 21, thevideo-frequency impulses indicated at V having been supplied fromthecathode-ray signal generator I4 by way of amplifiers 26 and 21 andthe line and frame pedestals pl and pf having been supplied from thegenerator l8 and mixed with the video signal in the amplifier 21. Thecurve of Fig. 8 represents the line-synchronizing impulse wave developedby the generator l9, while the curves of Figs. 9 and 10 represent thealternate line-frequency impulse wave and parabolic impulse wave, thelatter being at double the line frequency developed by the generators 20and 2 |-2lc, respectively. As explained above. with reference to Figs.12/16, inclusive, the alternate line impulses are timed to'occurintermediate the line-synchronizing impulses, while the parabolicimpulses "are timed to occur between succeeding impulses when theline-synchronizing and alternate-line impulse waves are combined.

The final desired modulation signal developed by the system is of thewave form shown in Fig. 11. To develop such a wave, theline-synchronizing impulses are repeated continuously by the tube 34 andare doubled by adding the alternate line-frequency impulses during apart of the retrace portion of each field-frequency cycle, which portioncorresponds to the duration of the field pedestal. During a part'of theline doubling period, the parabolic impulses are inserted between thedoubled impulses to provide, in eflect, relatively long, serrated,field-synchronizing impulses for each field cycle without interruptionof the line-synchronizing impulses, and the combined synchronizingsignal is combined with the video signal.

It is necessary that the alternate and parabolic impulses be added tothe line-synchronizing impulses only during predetermined portions ofeach frame cycle. In Figs. '1 and. 11, points a: and x correspond to thebeginning and termination of a frame pedestal impulse such as suppliedby the pedestal generator It. The line doubling, or addition of thealternate-impulse wave, takes place between the points 11 and 11', theinitiation of this action being delayed for the period rep-' resented atd1 while the addition of the parabolic impulses takes place between thepoints z and z, the initiation of the latter action being delayed for aperiod represented at da.

The output circuits of the tubes 34, 35, and 36 being connected inparallel, when these tubes are conductive, the'signals impressed ontheir input circuits are combined in their common output circuit. 'I'hetube 34 continuously repeats the line-synchronizing impulses (Fig. 8)received from generator l9. However, the tubes 35 and 36 are normallybiased beyond cutofi by the fixed ,chronize the operation biases appliedto their suppressor grids. The periodic rectangular impulses developedby the oscillators Ba and I3b, delayed by intervals d1, dz,respectively, in a manner corresponding to that illustrated in Figs.3-5, inclusive, however, are applied positively to the grids of thetubes 35 and 35, respectively, and serve to unblock these tubes for thedurations 11-11, 2-2, respectively, ofthe impulses, so that the signalsapplied to their control grids from the generator 20 and limiter andamplifier 2lc, respectively, are repeated only during the intervals11-11, 2-2, respectively, in the common output circuit and are combinedwith the line-synchronizing impulses. Due to the predetermined delayseffected by the 1 delay apparatus of the present invention and thecontrol of the duration of the rectangular-impulse waves generated bythe oscillators l3a and l3b, the alternate-and parabolic impulses arethus mixed with the line impulse during the precise desired part of theretrace portion of each frame 6 cycle, initiating at points delayed withrespect to the starting point a: in the frame pedestal. The

. combined synchronizing signal is supplied to the therein mixed withthe video amplifier 28 and modulation signal of signal, and theresultant the desired form shown in Fig. 11 tained.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modi- 1. A periodic-impulsewave-generating systemcomprising means for deriving from a firstperiodic-impulse wave of a predetermined frequency a secondperiodic-impulse wave having impulses initiating at the occurrences ofthe impulses of said first wave and of predetermined durationindependent of the duration of the impulses of said first wave, andmeans coupled to said first means for synchronization by the wavedeveloped thereby for developing a third periodic-impulse wavecomprising impulses initiating at the termination of the impulses ofsaid second wave and having a duration independent of: the duration ofany of 2'. A periodic-impulse wave-generating system comprising a firstgenerator adapted to be synchronized bya periodic-impulse wave of apredetermined frequency for' developinga periodicrectangular-impuls'ewave comprising impulses impulses of said first wave and ofpredetermined duration independent of the duration of the impulses ofsaid first wave, a second generator for developing a periodic-impulsewave of said predetermined frequency, the duration of the impulses ofthe .wave of said second generator being independent of the duration ofany of the other of said impulses and means coupling said secondgenerator to said first generator to synthereof and thereby to initiatethe impulses of the wave developed by said second generator at theoccurrences of the trailing edges of said rectangular impulses.

3. A periodic-impulse wave-generating system comprising means forderiving from a periodicimpulse wave of predetermined frequency aperiodic-rectangular impulse wave having impulsesfall within the truespirit the other of said impulses.

is thus obhaving their leading edges initiating with the initiating onthe occurrence of the impulses of the first said wave and oipredetermined duration independent of the duration of the impulses ofsaid first wave, means for deriving from said rectangular-impulse wave aperiodic-impulse wave having double impulses, the first and secondimpulses of each cycle of whichoccur, respec tively, with the leadingand trailing edges of one of said rectangular impulses, and meanscoupled to said double-impulse generating means for developing aperiodicimpulse wave having impulses initiating on the occurrences ofthe second of said double impulses and' having a duration independentofthe duration of any of theother of said impulses.

4. A periodic-impulse wave-generating system comprising means forderiving from a periodicimpulse wave of a predetermined frequency aperiodic-rectangular current-impulse wave hav--- ing impulses initiatingon the occurrence of the impulses of said first wave and ofpredetermined duration independent of the duration of the impulses ofsaid first wave, current-diiferen tiating means for deriving from saidrectangularcurrent-impulse wave a periodic-impulse wave having doublevoltage impulses, the first and second impulses of each cycle of whichoccur, respectively, with the leading and trailing edges of one of saidrectangular impulses, and means coupled to said double-impulsegenerating means for developing a periodic-voltage-impulse wave havingimpulses initiating on the occurrences of the second of said doubleimpulses and having a duration independent of the duration of any-of theother of said impulses.

5. A periodic-impulse wave-generating system comprising a source ofperiodic-voltage-impulse waves of predetermined frequency, a relaxationoscillator for developing a periodic-rectangular current-impulse wavehaving impulses of predetermined duration independent of the duration ofthe impulses of said first wave, means coupling said oscillator to saidgenerator for synchronizing said oscillator to initiate said rectangularimpulses on the occurrence of the impulses of said first wave,current-differentiating means for deriving from saidrectangular-current-impulse wave a periodic-impulse wave havingdoublevoltage impulses, the first and second impulses of each cycle ofwhich occur, respectively, with the leading and trailing edges of one ofsaid rectangular-current impulses, a relaxation oscillator fordeveloping a 'periodic-voltage-impulse wave at said predeterminedfrequency, and means coupling said last-mentioned oscillator to saiddifi'erentiating means for synchronizing the operation thereof toinitiate the occurrences of the impulses of the wave developed therebyat the occurrences of the second of said double-voltage impulses.

6. In a television system, a synchronizing-signal generator comprisingmeans for developing a periodic-impulse wave of a predeterminedfrequency, means for deriving from said wave a second wave havingimpulses initiating on the occurrence 01' the impulses of said firstwave and of predetermined duration independent of the duration of theimpulses of said first wave, means coupled to said first means forsynchronization by the wave developed thereby for developing aperiodic-impulse-control wave having impulses init ating at thetermination of the impulses of sai second wave and having a durationindependent of the duration of any of the other of said impulses, aplurality of separate periodicimpulse wave generators, means forcombining the signal outputs of said plurality of generators to developa single synchronizing signal, and means for'utilizing said control wavefor controlling the operation of said combining means.

7. In a television system, a synchronizing-signal generator comprisingmeans for developing a periodic-impulse wave of a predeterminedfrequency, means for deriving from said wave a. second wave havingimpulses initiating on the occurrence of the impulses of said first waveand of predetermined duration independent of the duration of theimpulses of said first wave, means coupled to said first means forsynchronization by the wave developed therebyfor developing aperiodic-impulse-control wave having impulses in tiating at thetermination of'the impulses of said second wave and having a durationindependent of the duration of any of the other of said impulses, aplurality of separate periodicimpulse wave generators, means forcombining the signal outputs of said plurality of generators to developa single synchronizing signal, and

means for utllizing'said control wave to control the duration of, andeffect a phase delay in, the operation of said combining means.

8. In a television system, a synchronizing-signal generator comprisingmeans for developing a timing periodic-impulse wave 01' a predeterminedfrequency, a plurality of separate control networks each comprising. afirst means for deriving from said timing wave a second wave havingimpulses initiating onthe occurrence of the impulses of said timing waveand of predetermined durations independent 01' the duration of theimpulses of said first wave, means coupled to said first means forsynchronization by the wave developed thereby for developing aperiodic-impulse-control wave having impulses initiating at thetermination of the impulses of said second wavesand having a durationindependent of the duration of any of the other of said impulses, a

plurality of separate periodic-impulse wave gen- 9. In a televisionsystem, a synchronizing-sig-.

nal generator comprising means for developing a periodic line-scanningimpulse'wave of a predetermined frequency, means for developing analternate periodic-impulse wave or said predetermined frequency andhaving impulses occurring intermediate said line-scanning impulses,means for developing a perlodic-parabolic-impulse vwave of double saidpredetermined frequency and having impulses occurring between saidline-scanning and alternate, impulses, means for developing a periodicframe-frequency impulse wave of a predetermined frequency less thansaidline frequency, means for combining said alternate and parabolic-impulsewaves with said line 1mpulse waves, means for deriving from saidframefrequency wave a periodic-impulse wave having impulses occurring atthe initiation of said frameirequency impulses and of predeterminedduration, and means coupled to said last-mentioned means forsynchronization thereby for developing a periodic-impulse-control wavehaving impulses initiating at the termination of the impulses of saidlast-mentioned wave, and means for utilizing said control wave foreffecting operation of said combining means only during apredeterminedperiod of each frame-frequency cycle delayed with respect to theinitiation of the frame-scanning impulse.

10. In a television system, .a synchronizing-signal generator comprisingmeans for-developing a periodic line-scanning impulse wave of apredetermined frequency, means for developing an alternateperiodic-impulse'wave of said predetermined frequency and havingimpulsesoccurring intermediate said line-scanni g impulses, means fordeveloping a periodic-para olic-impulse wave of double saidpredetermined frequency and having impulses occurring between saidline-scanning and alternate impulses, means for developing a periodicframe-frequency impulse wave of a predetermined frequency less than saidline frequency, means for developing a periodic-pedestalimpulse wave atsaid frame frequency and having impulses of predetermined durationinitiatingat said frame-frequency impulses, means for combining saidalternate and parabolic impulses with said line impulses, two separatemeans for controlling said combining means each including means forderiving from said frame-frequency impulses a first periodic-impulsewave having impulses occurring on the initiation of said framefrequencyimpulses and of predetermined duration and means coupled to thelast-mentioned means for synchronization by the wave developed therebyfor developing a periodic-control-impulse wave comprising impulsesoccurring at the termination of the impulse of said first wave, meansfor utilizing one of said control waves to effect operation of saidcombining means with respect to said alternate impulses forpredetermined periods corresponding to a given portion of saidframe-pedestal impulses and delayed with respect to said frame-frequencyimpulses, means for utilizing the other of said control means to effectthe operation of said combining means with respect to said parabolicimpulses for predetermined periods corresponding to a. given portion -ofsaid first-mentioned portions of said framepedestal impulses and delayedwith respect to said frame-frequency impulse for a period greater thansaid first-mentioned delay, and meansfor combining the output of saidcombining means with said pedestal-impulse wave.

11. A periodic-impulse wave-generating system comprising means fordeveloping a first periodic wave of predetermined frequency, means. forderiving from said first wave a periodic line-scanningrectangular-impulse wave of half said predetermined frequency, means forderiving, from said first wave an alternate periodic-rectangular-'impulse wave of half said predetermined frequency and having impulsesoccurring intermediate said line-scanning impulses, means for derivingfrom said first wave a periodic-parabolicimpulse wave of saidpredetermined frequency and having impulses occurring between saidlinescanning and alternate impulses, and means for combining saidline-scanning, alternate, and parabolic-impulse waves.

12. A periodic-impulse wave-generating system comprising means fordeveloping a first periodic wave of a predetermined frequency, means forderiving from said first wave a periodic linescanningrectangular-impulsewave of half said predetermined frequency, means for deriving from saidfirst wave an alternate periodic-rectangular-impulse wave of half saidpredetermined frequency and having impulses occurring intermediate saidline-scanning impulses, means for deriving as an infinitesimal calculusfunction of said first wave a parabolic-impulse wave of saidpredetermined frequency and having impulses oc-' curring between saidline-scanning and alternate impulses, and means for combining'saidlinescanning, alternate, and parabolic-impulse waves.

13. In a television system, a synchronizing-' signal generatorcomprising means for developing a periodic line-scanningrectangular-impulse waveof a predetermined frequency, means fordeveloping an alternate periodic-rectangular-impulse wave of saidpredetermined frequency and having impulses occurring intermediate saidlinescanning impulses, means for developing a periodic-parabolic-impulsewave of double said predetermined frequency and having impulsesoccurring between said line-scanning and alternate impulses, means forperiodically combining said predetermined periods, and means forperiodically combining said parabolic wave with the combinedline-scanning and alternate waves for predetermined periods comprisinggiven portions of said first-mentioned predetermined periods.

14; In a television system the combination of means for developing aperiodic frame-pedestal .impulse wave of a predetermined frequency,

means for developing a periodic line-scanning rectangular-impulse waveof a predetermnied frequency, means for developing an alternate peri-.alternate wave with said line-scanning wave for of said frame-pedestalimpulses, means for com- I bining said parabolic-impulse wave withsaidcombined line-scanning and alternate waves for predetermined periodscomprising given portions of said first-mentioned predetermined periods,and means for combining said combined line-scanning, alternate, andparabolic waves with said frame pedestal-impulse wave.

15. A periodic-impulse wave-generating system comprising means fordeveloping a first periodic wave of a predetermined frequency and ofsawtooth wave. form and including. trace and retrace portions, means for'deriving as an infinitesimal calculus function of said saw-tooth wave aperiodic wave of said predetermined frequency and of parabolic waveform, and means for limiting and amplifying said last-named wave toderive therefrom a periodic wave of said predetermined frequencycomprising only parabolic impulses occurring during the trace portionsof said sawtooth wave. a

16, A periodic-impulse wave-generating system comprising means fordeveloping a first periodic wave of a predetermined frequency and ofrectangular-impulse wave form, means for deriving frorr.

' said saw-tooth wave trace portions, and means for limiting saidparabolic wave to derive a periodic wave of said predetermined frequencycomprising only parabolic impulses occurring intermediate saidrectangular impulses of said first wave. l

17. The method of developing a periodic-impulse wave having impulsesdelayed in phase with respect to the impulses of a firstperiodic-impulse wave, which comprises deriving from said first wave asecond periodic-impulse wave having impulses initiating on theoccurrence of the impulses of said first wave and of predeterminedduration independent of the duration of the impulses of said first wave,and deriving from said second wave a third periodic-impulse wavecomprising impulses initiating'at the termination of the impulses ofsaid second wave and having a duration independent of the duration ofany of the other of said impulses.

l8. The method of developing a periodic-impulse wave having impulsesdelayed in phase with respect to impulses of a first periodic-impulsewave, which comprises deriving from said first wave a secondperiodic-impulse wave having rectangular impulses initiating on theoccurrence of the impulses of said first wave and of predeterminedduration independent of the duration of the impulses of said first wave,diilerentiating said rectangular-impulse wave to derive a thirdperiodic-impulse wave having double impulses, the first and secondimpulses of each cycle of which occur, respectively, with the leadingand trailing edges of said rectangular impulses, and deriving from saidthird wave a fourth periodic-impulse wave having impulses initiating onthe occurrence of the second of said double impulses and having aduration independent of the duration of any of the other of saidimpulses.

l9. Ihe method of developing a television synchronizing-impulse wavewhich comprises developing a first periodic line-scanningrectangular-impulse wave of a predetermined frequency, developing analternate periodic-rectangular-impulse wave of said predeterminedfrequency and having impulses occurring intermediate said linescanningimpulses, developing a periodic-parabolic-impulse wave of double saidpredetermined frequency and having impulses occurring between saidline-scanning and alternate impulses, peri odically combining saidalternate wave and said line-scanning wave for predetermined periods,and periodically combining said parabolic wave with the combinedline-scanning and alternate waves for predetermined periods comprisinggiven portions of said first-mentioned predetermined periods.

20. The method of developing a television signal which comprisesdeveloping a periodic framepedestal impulse wave of a predeterminedfrequency, developing a periodic line-scanning rectangular-impulse waveof a predetermined frequency, developing an alternate periodic-rectan-'gular-impulse wave of said predetermined linescanning frequency andhaving impulses occurring intermediate said line-scanning impulses,developing a periodic-parabolic-impulse wave of double saidpredetermined frequency and having impulses occurring between saidline-scanning and alternate impulses, periodibally combining saidalternate wave with said line-scanning wave for' predetermined periodscomprising given portions of said frame-pedestal impulses, combiningsaid parabolic-impulse wave with said combined linescanning andalternate waves for predetermined periods comprising given portions ofsaid firstmentioned predetermined periods, and combining said combinedline-scanning, alternate, and parabolic waves with said frame-pedestalimpulse wave.

MADISON CAWELN.

